Mixing and frothing device and method

ABSTRACT

The invention relates to a mixing device with an input container that is configured for receiving a product that includes a fluid component and a second component. A whipper with a conical whipper surface has an axis is configured for aerating and frothing the product. The whipper surface extends between first and second end portions, with the first end portion having a smaller diameter than the second end portion. The whipper surface is preferably oriented at a surface angle to the axis of about between 5° and 65°. A motor is in driving association with the whipper for rotating the whipper about the axis at a speed sufficient for aerating and frothing the product. A product exit conduit is disposed downstream of the whipper and is configured for dispensing the product of the fluid and second components.

FIELD OF THE INVENTION

[0001] The present invention relates to a mixing device that provides afrothy fluid product. More particularly, the invention relates to amixing device for mixing, frothing, and dispensing a beverage, and to amethod for providing a frothy fluid product.

BACKGROUND OF THE INVENTION

[0002] Espresso and other coffee and milk drinks are often prepared bymixing a powder in water. Traditionally, a milk froth is provided to thedrink by steam frothing.

[0003] Mixing devices are known for speedier preparation of suchbeverages and other foods by mixing a powdered food component with aliquid, such as water. These devices typically feed the powderedcomponent into the water, which is often pumped tangentially into amixing chamber to create a whirlpool to mix the powder into the water.The mixture is then fed to a whipping mechanism, which is usually arotating plate. The plate aerates the mixture and produces a froth. Thefrothed mixture is usually dispensed into a container for drinking.

[0004] U.S. Pat. No. 5,927,553, for example, discloses a mixing anddispensing apparatus with a cruciform frothing blade. Other shapes offrothing blades are also known. For instance, companies such as Rhea andZanussi use whippers with an axially short disk with very steep slopedwalls. Other whippers have rotors with independent ramps extending froma substantially flat plate. The known devices generally have theirgreatest efficiency for preparing a small group of products.

[0005] There is a need for a mixing device with an improved frothingeffect and efficiency. The present invention satisfies this need.

SUMMARY OF THE INVENTION

[0006] The invention relates to a mixing device with high versatility,as it is able to very effectively aerate and froth different products,such as coffee and milk products, for serving in a cup. A preferredembodiment of the device has an input container configured for receivinga product that comprises a fluid component and a second component. Awhipper is provided in a housing of the device with a conical whippersurface that has an axis and that is configured for aerating andfrothing the product. The whipper surface extends between first andsecond end portions of the whipper. The first end portion has a firstdiameter and is in fluid communication with the input container toreceive the product. The second end portion is disposed downstream ofthe first end portion and has a second diameter that is larger than thefirst diameter. The whipper surface of this embodiment is oriented at anangle to the axis of about between 5° and 65°, more preferably aboutbetween 10° and 45°, and most preferably about between 15° and 35°. Acontrolled shear gap is defined between the whipper surface and thehousing to provide a sufficient flow rate and energy transfer to themixture for a desired foaming effect. The perpendicular shear gap has awidth of about between 0.4 to 1.1 mm. A motor is in driving associationwith the whipper for rotating the whipper about the axis at a speedsufficient for aerating and frothing the product. Additionally, aproduct exit conduit disposed downstream of the whipper and configuredfor dispensing the product of the fluid and second components.

[0007] In the preferred embodiment the second diameter of the whipperrotor is at least about 10% larger than the first diameter. Morepreferably, the second diameter is between about 1.25 and 2.5 times thesize of the first diameter. The preferred axial length of the whippersurface about between a quarter and twice the size of the firstdiameter.

[0008] Also, the motor and whipper of the preferred embodiment areconfigured for providing an energy dissipation to the product of aboutbetween 1 J/g and 2.5 J/g with a product flow rate of about between 5g/sec and 30 g/sec. The energy dissipation is preferably selectively inat least the range of about 0.5 J/g to 1.5 J/g with a product flow rateof about between 5 g/sec and 30 g/sec.

[0009] The conical surface of this embodiment has a substantiallyconstant surface angle between the first and second end portions, butthe surface angle can vary along the length of the whipper surface. Awhipper housing preferably has a shape corresponding to the whippersurface. In addition, the whipper surface of one embodiment definesgrooves extending between the first and second ends.

[0010] To obtain the frothing effect desired, and depending on themixture of components fed into the device, a preferred motor controlleris configured for selective operation at various speeds. In oneembodiment, the motor controller is configured for varying the rotationspeed of the motor between first and second speeds during the productionof a single product.

[0011] A first wall member is preferably disposed downstream of andfacing the second end of the whipper in a preferred embodiment. Thefirst wall member is spaced from the second end by about between 0.25 mmand 5 mm, and more preferably by about between 1 mm and 3 mm. In thepreferred embodiment, the first wall member includes at least one ribextending radially with respect to the axis and protruding towards thewhipper and configured for increasing the efficiency of the frothing ofthe product. Preferably, a plurality of ribs is provided, and morepreferably, there are between two and eight ribs to increase efficiencyin frothing. The preferred height of the ribs from the back wall of thewall member is about between 0.5 mm and 4 mm, and preferably the ribsare spaced from the second end by about between 0.25 mm and 5 mm. Theback wall itself is preferably sloped away from the whipper in aradially outward direction to improve the outwards radial flow of theproduct.

[0012] The preferred embodiment includes a support member configured forsupporting the input container. The support member may include amounting member attachable to a support wall or other support element.The support member also preferably includes a second bayonet attachmentportion configured for releasably engaging a first bayonet attachmentportion of the input container to attach the input container to thesupport member. Preferably, one of the bayonet attachment portionscomprises a cam ramp, and the other comprises a latch. A resilientmember is preferably associated with the input container and supportmember for biasing the input container away from the support member whenthe bayonet attachments are released from each other to facilitate theseparation of these parts. This arrangement allows easy removal andreplacement of the input container for clearing.

[0013] To prepare a beverage, a user preferably introduces milk powderand a diluent into a shear gap defined adjacent a tapered whippersurface that has an axis and that extends between first and secondsurface ends. The first surface end in this preferred method has a firstdiameter of at least about 18 mm, and the second surface end is disposeddownstream of the first surface end and has a second diameter that islarger than the first diameter. The whipper surface is oriented at asurface angle to the axis of less than 90° to extend the whippingsurface with a sufficient length and surface area to provide a highfrothing efficiency. The whipper is rotated to mix, aerate, and froththe milk powder and diluent to produce a frothed beverage having a ratioof froth volume to liquid volume of at least about 60%. The milk powdermay comprise, for example, a medium heat milk powder, preferably a skimmilk powder.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a perspective view of a preferred embodiment of theinvention;

[0015]FIG. 2 is a cross-sectional view thereof; and

[0016]FIG. 3 is an exploded view thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Referring to FIGS. 1 and 2, a preferred embodiment of theinvention is a mixing device 10 that includes an input container 12. Theinput container 12 comprises a bowl portion 14 with a tangential inlet16 for feeding a fluid under pressure. An automatically controlled valveis preferably provided to control the fluid flow into the inputcontainer 12. The fluid is introduced through the inlet at a speedselected to produce a swirling flow, preferably substantially awhirlpool effect.

[0018] A component to be mixed with the fluid, preferably a powderedfood substance, is fed into powder inlet 18, which preferably includesan opening at the top of the bowl portion 14. The powder can be fed byhand or automatically by a powder source, preferably disposed above thedevice 10. The powder source preferably has a dosing mechanism, such asa dosing screw, to automatically dose a predetermined amount of powderinto the input container 12. A lip 20 extends around the interior of thepowder inlet 18, protruding into the bowl portion 14 to prevent theswirling fluid from exiting the input container 12 by the upper sidethereof. A suction is applied to orifice 21, connected to the undersideof the lip 20 for extracting any splashed material. The powder inlet issufficiently large to receive the powder poured therein and also toreceive a sufficient amount of air for mixing with the fluid andcomponent.

[0019] In the embodiment shown, a throat portion 22 of the inputcontainer 12 is disposed below the bowl portion 14. The throat portion22 preferably has a narrower diameter than the bowl portion 14 and has athroat opening 24 disposed on a lateral side, as shown in FIG. 2. Thethroat portion 22 is preferably generally coaxial with the bowl portion14 and narrows substantially evenly along the axis of the bowl portion14. This improves the fluid flow therein and reduces any trapping ofpowder. Preferably, a transition between the bowl portion 14 and thethroat portion 22 has an inward bend 25, followed by a sloped portion27, which is followed by an outward bend 29, in cross-section.

[0020] Referring to FIGS. 2 and 3, a whipper assembly 26 is in fluidcommunication with the input container, preferably at the throatopening. The whipper assembly includes a whipper rotor 28. A motor 30drives rotor shaft 32, which drives the whipper rotor 28 so that themotor 30 drives the whipper at about whipper axis 34. A motor controlleris preferably provided to control the operation and speed of the motor30.

[0021] The preferred whipper rotor 28 has a conical whipper surface 36.The conical surface 36 preferably faces outwardly with respect to thewhipper axis 34 and can have a substantially straight cross-section, asin the embodiment shown, or can be curved in cross-section with a taperangle that varies along the axial length of the whipper rotor 28. Thewhipper surface in the embodiment shown extends at a surface angle 42 tothe whipper axis 34. Surface angle 42 is the average angle between firstand second surface end-portions 38,40, and the whipper surface 36 ispreferably substantially continuous about its circumference between theend portions 38,40. The angle may change beyond the end portions 38,40.Surface angle 42 is preferably about between 5° and 65°, more preferablyabout between 10° and 45°, still more preferably about between 15° and35°, and most preferably about between 20° and 30°.

[0022] The preferred whipper surface 36 extends substantially betweenfirst and second end portions 38,40. As the whipper surface 36 isconical or tapered, the first surface end portion 38 has a smallerdiameter than the second surface end portion 40. The first end portion38 preferably faces the interior of the input container 12, with thesecond end portion 40 disposed on an opposite side of the whippersurface 36. In the preferred embodiment, diameter of the second endportion 40 is at least about 10% the first end portion 38 diameter. Morepreferably, second end portion diameter is about between 1.25 and 2.5times the size of the first diameter. The whipper surface 36 preferablyhas an axial length of about between a quarter and twice the size of thefirst end portion diameter. In one embodiment, the first end portiondiameter is about between 18 to 25 mm, and the second end portiondiameter is about between 30 and 35 mm, with an axial length between theend portions of between about 10 and 25 mm. The diameters of the whipperrotor, including of the end portions are preferably measured to widestpoint at the station being measured along the axis 34. Thus, thediameter of a rotor with protrusions, such as ribs, is measured to thetip of the protrusions. Preferably, however, any protrusions of grooveson the surface are not deeper than about 6 mm in the preferredembodiment.

[0023] The whipper surface preferably has a surface area of at leastabout 800 mm² and more preferably at least about 100 mm², and preferablyat most about 3000 mm² and more preferably at most about 2000 mm². Thissurface area is calculated taking the cross-sections of the surface asbeing circular and having the diameter of the whipper rotor at therelevant axial stations as described above.

[0024] Additionally, in the embodiment shown, the surface end portions38,40 are located at the extreme ends of the frustoconical whipper rotor28. In other embodiments, the surface end portions may me locatedremotely from the ends of the whipper. In one embodiment, the first,smaller surface end 38 is defined as being at the portion of the taperedwhipper rotor where the diameter becomes at least about 18 mm. Thus,this embodiment has a whipper surface measured from the location on thewhipper rotor where the diameter becomes at least about 18 mm. Thisalternative embodiment may also have a second surface portion of thewhipper rotor that extends in the direction away from the second end,and which can be continuous and can follow the adjacent whipper surface.The second surface portion may extend to the most upstream end of thewhipper rotor. In another embodiment, the surface portion is measuredfrom the location on the whipper rotor where the diameter becomes atleast about 20 mm, and in yet another embodiment, it is measured fromthe location on the whipper rotor where the diameter becomes at leastabout 25 mm.

[0025] In the preferred embodiment, first or front whipper face 44preferably defines a recessed portion 46, preferably in the shape of anannular groove, facing the interior of the input container 12. A secondor rear whipper face 48 also preferably includes a recessed portion 50facing in an opposite direction from the front face 44. In the drawings,the first and second whipper faces are disposed at the first and secondsurface ends 38,40. In the alternative embodiment described in which oneor both of the surface ends is located remotely from the end of thewhipper rotor itself, one or both of the surface ends and the whipperfaces, respectively, are also disposed remotely from each other.

[0026] The whipper rotor 28 is disposed within a whipper housing 52,which in the embodiment shown is integral part of unitary constructionwith the input container 12. The preferred whipper housing 52 has aninner housing surface 54 with a shape substantially corresponding to thewhipper surface 36. A shear gap 56 is defined between the housingwhipper surfaces 54,36 that has a width selected to provide a sufficientflow rate and energy transfer to the mixture, for a desired foamingeffect. Measured in a direction parallel to the whipper axis, 34, theshear gap 56 is preferably at least about 0.5 mm, more preferably atleast about 0.8 mm, and most preferably at least 1 mm. Measures in thisdirection, the shear gap 56 is preferably at most about 2.5 mm and morepreferably at most about 1.5 mm. One embodiment has a shear gap in thisrange with a surface angle 42 of about 25°. In a direction orthogonal tothe whipper surface 36, the preferred size of the perpendicular sheargap is at least about 0.4 mm, and at most about 1.1 mm. The conicalshape of the whipper rotor 28 provides a long shear gap 56 for acting onthe fluid mixture, while providing a pumping action and withoutrequiring an extremely large radius.

[0027] As shown in FIG. 3, the whipper rotor surface 36 preferablydefines a plurality of rounded grooves 70, preferably extending betweenthe first and second end portions 38,40. The preferred grooves 70 aretwisted to spiral along the length of the whipper rotor 28. The grooves70 of the present embodiment are about between 0.5 and 3 mm deep. Thegrooves 70 are preferably configured and dimensioned for increasing thefrothing action of the fluid mixture. In an alternative embodiment, thegrooves are substantially aligned with the whipper axis 34, and inanother embodiment, there are no grooves. The motor can turn the whipperrotor 28 in or against the direction of the grooves depending on thepumping and frothing effect desired.

[0028] A wall member 57 includes a back wall 58 is disposed behind thewhipper rotor, facing the second end 40 portion and the rear whipperface 48. The preferred back wall 58 includes protrusions, which arepreferably at least one rib 60 that protrude towards the whipper rotor28. The ribs 60 in the embodiment shown extend radially substantially ina straight line, with substantially uniform thickness. In anotherembodiment, the ribs can extend along curved lines.

[0029] Preferably, the back wall 58 has at least two ribs 60, and morepreferably it has more than two ribs 60. The back wall 58 preferably hasup to eight ribs 60, and more preferably up to six ribs 60. The forwardside 62 of the ribs 60 facing the whipper rotor 28 preferably has arounded cross-section, although other shapes may be suitable as well.Additionally, the rib forward edge 62 of the illustrated embodiment issubstantially straight when viewed from the side, as in FIG. 2, whichshows a cut parallel to the longitudinal or radial length of the ribs60. In alternative embodiments, the ribs 60 may generally follow theshape of the back wall 58 or may have a different shape.

[0030] The preferred back wall 58 itself is not flat, but issubstantially flat in a alternative embodiment. A central portion 64 ofthe back wall 58 shown extends in the direction of the whipper rotor 28and is sloped away from the whipper rotor 28 towards the radial edgeportion 66 of the back wall 58. The sloped portion 68 shown extends fromthe central portion 64 over most of the radius of the back wall 58.Preferably, the sloped portion 68 extends beyond the radius of thesecond end portion 40 of the whipper rotor 28, or the portion of thewhipper rotor 28 that is unobstructed with respect to the back wall 58.The radial edge portion 66 of the back wall 58 in contact with the fluidis preferably curved along a radial cross-section to slope in a reversedirection from the sloped portion 68. This curvature and reverse slopeof the radial edge portion 66 substantially reduces or preferablysubstantially eliminates sharp angles in which the fluid will be trappedor restricted. The combination of the slopes of the sloped portion 68and radial edge portion 66 improves the efficiency of the fluid flow.

[0031] The whipper rotor 28 is preferably spaced from the wall member57. In the preferred embodiment, the second end portion 40 of thewhipper rotor 28 is spaced from the rib forward edge 62 by at leastabout 0.25 mm, more preferably at least about 0.5 mm, and mostpreferably at least about 1 mm. The spacing between the whipper rotor 28and the rib forward edge 62 is preferably at most about 5 mm, morepreferably at most about 4 mm, and most preferably at most about 3 mm.The most preferred embodiment has a spacing of about 1.5 mm. Thisspacing is selected to limit and control the bubble size of air that isaerated into the fluid mixture. The height of the ribs 60 from the backwall 58 substantially adjacent the shear gap 56 is preferably at leastabout 0.5 mm, more preferably at lest about 1 mm, and most preferably atleast about 1.5 mm. The rib height is preferably at most about 4 mm,more preferably at most about 3 mm, and most preferably at most about2.5 mm.

[0032] The back wall 58 preferably has a larger outer diameter than thewhipper rotor 28, preferably at least about 10% larger and morepreferably at least about 20% larger, and most preferably at most about60% larger, and more preferably at most about 40% larger. The outerdiameter of the back wall 58 of the preferred embodiment is at leastabout 40 mm and at most about 60 mm. The preferred volume between theback wall 58 and the whipper rotor 28 is about between 2 ml and 12 ml,and more preferably about between 4 ml and 7 ml.

[0033] A product exit tube 72 is disposed downstream of the whipperrotor 28 and back wall 58 and is disposed to dispense the foamed fluidmixture. The product exit tube 72 is shown as an integral part ofunitary construction with the input container 12. The product exit tube72 preferably comprises a conduit with a diameter selected according tothe final product that is to be dispensed. The preferred product exittube 72 has an internal diameter of about between 2 mm and 5 mm forembodiments intended to prepare several different milk and coffeebeverages. Embodiments intended primarily for coffee preferably have aproduct exit tube 72 with an internal diameter of about between 1 mm and3 mm, and in embodiments intended primarily for milk, the internaldiameter is preferably from about 4 mm to 8 mm. The diameter of theproduct exit tube 72 is selected to obtain the desired pumpingperformance from the whipper rotor 28. Increasing the diameter of theconduit allows a faster flow, while decreasing the diameter providesmore back-pressure to retain the fluid mixture in the whipper assemblyand input chamber 12 for a longer time. A dispensing spout 75 ispreferably attached at the end of the product exit tube 72 for easierdispensing into a cup.

[0034] A seal, such as o-ring 90, seals the space between the inputcontainer 12 and the wall member 57 and product exit tube 72 area. Adrainage channel 73 behind and below the o-ring 90 is also provided tokeep any fluid that leaked past the o-ring 90 from contacting the motor30.

[0035] Referring to FIG. 3, the preferred embodiment has a supportstructure that comprises a support wall 74 that is disposedsubstantially vertically. The support wall 74 defines an opening 76 thatis contoured and configured for attaching and supporting the motor 30mostly on one side of the support wall 74, and the product handlingportion of the device, including the input container 12, the whipperrotor 28, and the product exit tube 72. Tabs 78 and recesses 80 in theopening 76 correspond with the shape of the mounting member 82, whichmounts to the support wall 74 and which supports and attaches most ofthe elements of the device to the support wall 74. The correspondingslopes help stabilize the elements and prevents rotation.

[0036] A quick-release/attach mechanism is preferably provided and, inthe embodiment shown, includes a retaining member 83, that comprises alatch member 84 that preferably slides along the mounting member 82 in acurved motion around input base 85 of the input container 12, which hasan axis that is parallel to the whipper axis 34. The embodiment shown isconfigured as a bayonet locking mechanism. The latch member 84 includesa handle 86 to enable a user to move the latch member 84 between releaseand locking positions, in which the input chamber is released or lockedto the mounting member 82, respectively. The input chamber preferablyhas at least one and preferably two or three cam ramps 88 disposed andconfigured for camming by the latch member 84 as the latch member 84 ismoved from the release to the locking position. A resilient or springmember, such as o-ring 90, is configured for and associated with themounting member and the input container 12 for biasing the inputcontainer away 12 from the mounting member 82 so that upon releasing thebayonet mechanism the spring member moves the input container away fromthe mounting member. This system allows a user to easily access theinput container 12, whipper rotor 28, and back wall 58 for cleaning,preferably without requiring substantial rotation of the input container12 itself. Other quick release mechanisms are suitable for embodimentsof the invention, such as other latching mechanisms in which the latchesmove along a differently shaped path, and in which the latches arereceived in receptacles. Also, the movable portion for locking the inputcontainer to the remainder of the structure can be mounted to the inputcontainer or another part of the device.

[0037] In use, the fluid is tangentially introduced into the inputcontainer 12 through tangential inlet 16. In the preferred embodiment,the fluid comprises water, and the flow rate is about between 3 mL/secand 30 mL/sec, more preferably about between 5 mL/sec and 15 mL/sec, andmost preferably about between 9 mL/sec and 12 mL/sec. At the time orpreferably after the water flow into the input container 12 iscommenced, a powdered food component, such as a powdered coffee productand/or powdered milk, is dosed into the water through powder inlet 18.Preferably the powder dosing begins at least about 0.1 sec after thewater dosing begins and more preferably at least about 0.3 sec. later,and preferably at most about 3 sec later, and more preferably at mostabout 1.0 sec later. Preferably the water is continued to be fed intothe input container 12 until the powder dosing is stopped, andpreferably at most about 8 sec after the powder dosing ends, and morepreferably at most about 3 sec later, and preferably at least about 1.0sec later.

[0038] The water and powder start getting mixed in the swirling flowwithin the input container 12, including the throat portion 22. Thewhipper rotor 28 is rotated by the motor 30 at a speed sufficient forpumping the mixture towards the product exit tube 72 and for producingthe desired foaming and aeration effect. The whipper rotor 12 sucks inair for incorporation into the mixture. The configuration and locationof the back wall 58 with respect to the whipper rotor 28 continued thefrothing effect, increasing the efficiency of the device. The rotationof the whipper rotor 28 and the shape of the back wall 58 centrifugallykeep the fluid product from accumulating behind the whipper rotor. Thespeed of the whipper rotor 12 is preferably variable to enable a speedselection to deliver the desired amount of energy to the mixture toproduce the desired frothing. For obtaining products of certainqualities, the rotation speed of the whipper rotor 28 is varied betweentwo or more speeds during the preparation of a single product. Table 1shows the preferred approximate energy dissipation and foam values fromthe device 10 for the listed products. The foam value is the volumeratio of foam to liquid in the resulting product. The coffee, espresso,and foamed coffee in the table are made from soluble coffee. The plainmilk, hot milk, and milk froth are reconstituted from soluble milk orcreamer. The milk froth is made from a medium heat milk powder, which isknown in the art and is made by heat treating skim milk at 85° C. to102° C. for between one and two minutes and then spray drying the heattreated milk or treated with an equivalent process. The quantity ofundenutured serum protein (whey protein) is between 1.5 and 6 mg pergram of the medium heat milk powder. TABLE 1 Foam Value Whipper RotorEnergy Dissipation (foam vol./ Product (rpm) (J/mL) liquid vol.) Plaincoffee 1,000-2,000 0.1-0.2 0%-5% Coffee 3,500-4,500 0.2-0.4 10%-15%Espresso 5,000-8,000 0.4-0.7 about 30% Foamed coffee  9,000-20,0000.8-2.5  40%-120% Plain milk 2,000-4,000 0.1-0.3 0%-5% Hot milk4,000-9,000 0.3-0.8 20%-40% Milk froth 10,000-15,000   1-2.5  60%-120%

[0039] The device 10 provides a high specific energy dissipation togenerate a milk froth and a moderately low specific energy dissipationto obtain a high quality coffee crema in the same unit. The frothedproduct is then dispensed through the product exit tube 72.

[0040] It has been found that to generate an authentic quality milkfroth when using a milk powder in a beverage dispenser, the specificenergy dissipation should be above about 1 J/g of product, whichincludes milk powder and water together. Authentic milk froth asreferred to in the present application is a frothed product with atleast an equal volume of milk foam compared to the volume of liquid. Themilk foam in the product having authentic milk froth preferably has adensity of about between 50 g/mL and 300 g/mL. An authentic cappuccinocan be made with the device of the present invention, which has a volumemade up by about ⅓ coffee, about ⅓ frothed milk foam, and about ⅓ ofmilk that remained liquid after frothing. The preferred milk fraction inthe authentic cappuccino has a volume that is at least as large as thevolume of the liquid portion. The foam of the frothed milk in the finalprepared beverage product is preferably stable, having at least about ⅔of the foam volume remaining after 10 minutes.

[0041] The energy dissipation of the device can be controlled byadjusting the shear gap, rotor speed, and product flow rate, althoughthese quantities are interdependent. A reduction in the shear gap, anincrease in rotor speed, and a decrease in flow rate will provide ahigher energy dissipation. The preferred flow rate is between at leastabout 5 g/sec and up to about 30 g/sec, and more preferably at leastabout 8 g/sec and up to about 15 g/sec. If the size of the gap isreduced, the flow rates will correspondingly be reduced and the amountof air drawn into the gap will be reduced as well, reducing foaming andaeration, and friction is increased. Also, if rpm is increased, noiseand cost of the machine will increase as well.

[0042] The preferred embodiments described above allow a device ofcompact size, and with a desirable flow rate for preparing individualdrinks to be provided without requiring extremely high rotor speeds,such as of above about 30,000 rpm. The preferred rpm used for foamedcoffee or milk froth are at most about 25,000, and more preferably atmost about 22,000. At these rotation speeds, the principal effectiveportion of the whipper rotor is that part of diameter of about 18 mm orgreater.

[0043] While illustrative embodiments of the invention are disclosedherein, it will be appreciated that numerous modifications and otherembodiments may be devised by those skilled in the art. For example, thewhipper rotor may have an inward facing whipper surface and rotate withrespect to a portion of the whipper housing that extends inside thewhipper. Therefore, it will be understood that the appended claims areintended to cover all such modifications and embodiments that comewithin the spirit and scope of the present invention.

What is claimed is:
 1. A mixing device, comprising: an input containerconfigured for receiving a product that comprises a fluid component anda second component; a whipper having a tapered whipper surface that hasan axis and that is configured for aerating and frothing the product,the whipper surface extending between first and second surface ends, thefirst surface end having a first diameter of at least about 18 mm andbeing in fluid communication with the input container to receive theproduct, and the second surface end being disposed downstream of thefirst surface end and having a second diameter that is larger than thefirst diameter, wherein the whipper surface is oriented at a surfaceangle to the axis of less than 90° to extend the whipping surface with asufficient length and surface area to provide a high frothingefficiency; a motor in driving association with the whipper for rotatingthe whipper about the axis at a speed sufficient for aerating andfrothing the product; and a product exit conduit disposed downstream ofthe whipper and configured for dispensing the product of the fluid andsecond components.
 2. The mixing device of claim 1, wherein the motorand whipper are configured for providing an energy dissipation to theproduct of about between 1 J/g and 2.5 J/g with a product flow rate ofabout between 5 g/sec and 30 g/sec.
 3. The mixing device of claim 1,wherein the motor and whipper are configured for providing an energydissipation to the product selectively in at least the range of about0.5 J/g to 1.5 J/g with a product flow rate of about between 5 g/sec and30 g/sec.
 4. The mixing device of claim 1, wherein the surface angle isabout between 5° and 65°.
 5. The mixing device of claim 4, wherein thewhipper surface has an area of about between 1000 mm² and 3000 mm². 6.The mixing device of claim 1, wherein the surface angle is about between10° and 45°.
 7. The mixing device of claim 1, wherein the whippersurface has an axial length of about between a quarter and twice thesize of the first diameter.
 8. The mixing device of claim 1, wherein theconical surface has a substantially constant surface angle between thefirst and second end portions.
 9. The mixing device of claim 1, whereinthe whipper housing has a shape substantially corresponding to thewhipper surface.
 10. The mixing device of claim 9, wherein a shear gapis defined between the housing and the whipper rotor, orthogonal to thewhipper surface, having a width of about between 0.4 mm and 1.1 mm. 11.The mixing device of claim 1, wherein the whipper surface definesgrooves extending between the first and second ends and having a depthof at most about 6 mm.
 12. The mixing device of claim 1, furthercomprising a first wall member disposed downstream of and facing thesecond end, the first wall member being spaced from the second end byabout between 0.25 mm and 5 mm.
 13. The mixing device of claim 12,wherein the first wall is spaced from the second end by about between 1mm and 3 mm.
 14. The mixing device of claim 1, further comprising amotor controller configured for selective operation at various speeds.15. The mixing device of claim 14, wherein the motor controller isconfigured for varying the rotation speed of the motor between first andsecond speeds during the production of a single product.
 16. A mixingdevice, comprising: an input container configured for receiving aproduct that comprises a fluid component and a second component; awhipper in fluid communication with the input container to receive theproduct and configured for mixing and frothing the product; a motor indriving association with the whipper for rotating the whipper about theaxis at a speed sufficient for mixing and frothing the product; a firstwall member disposed downstream of, facing, and spaced from the whipper,the first wall member comprising at least one rib extending radiallywith respect to the axis and protruding towards the whipper, the ribbeing configured for increasing the efficiency of the frothing of theproduct; and a product exit conduit disposed downstream of the whipperand configured for dispensing the product of the fluid and secondcomponents.
 17. The mixing device of claim 16, wherein the at least onerib comprises between 2 and 8 ribs.
 18. The mixing device of claim 16,wherein the wall portion comprises a back wall facing the whipper, andthe rib has a height from the back wall of about between 0.5 mm and 4mm.
 19. The mixing device of claim 16, wherein the rib is spaced fromthe second end by about between 0.25 mm and 5 mm.
 20. The mixing deviceof claim 16, wherein the first wall member is sloped away from thewhipper in a radially outward direction for improving the outwardsradial flow of the product.
 21. The mixing device of claim 16, whereinthe whipper comprises a conical whipper surface that has an axis andthat is configured for aerating and frothing the product, the whippersurface extending between first and second end portions, the first endportion having a first diameter and being in fluid communication withthe input container to receive the product, and the second end portionbeing disposed downstream of the first end portion and having a seconddiameter that is larger than the first diameter, wherein the whippersurface is oriented at a surface angle to the axis of about between 5°and 65°.
 22. A method of preparing a frothy beverage, comprising:introducing milk powder and a diluent into a shear gap defined adjacenta tapered whipper surface that has an axis and that extends betweenfirst and second surface ends, the first surface end having a firstdiameter of at least about 18 mm, and the second surface end beingdisposed downstream of the first surface end and having a seconddiameter that is larger than the first diameter, the whipper surfacebeing oriented at a surface angle to the axis of les than 90° to extendthe whipping surface with a sufficient length and surface area toprovide a high frothing efficiency; rotating the whipper surface to mix,aerate, and froth the milk powder and diluent to produce a frothedbeverage having a ratio of froth volume to liquid volume of at leastabout 60%.
 23. The method of claim 22, further comprising the shear gap,whipper surface, and rotation speed of the whipper surface for providingan energy dissipation to the product of about between 1 J/g and 2.5 J/gwith a product flow rate of about between 5 g/sec and 30 g/sec.
 24. Themethod of claim 22, wherein the milk powder comprises a medium heat milkpowder.
 25. The method of claim 22, wherein the milk powder comprises askim milk powder.